1. Field of the Invention
The present invention relates to an optical module for a motor vehicle lighting device of the projector type and more particularly, to optical modules referred to as elliptical modules comprising a light source associated with a reflector and closed by a dioptric element of the convergent lens type, for example a plano-convex type lens, or a Fresnel lens. The invention provides optical modules equipped with a fixed or movable shield capable of intercepting at least partially, according to its position, the light beam emitted by the light source/reflector assembly. The shape of the upper edge of the shield makes it possible to delimit the desired cut-off in the beam by imagery with the convergent lens.
2. Description of the Related Art
Besides these well-known lighting and signaling functions, new functions have recently appeared, grouped together under the name AFS (Advanced Front System), which offer in particular other types of beam functions. These functions concern in particular:                the so-called BL (Bending Light) function, which can be broken down into a so-called DBL (Dynamic Bending Light) function and a so-called FBL (Fixed Bending Light) function. The DBL function makes it possible to modify the orientation of a light beam produced by a light source so that, when the vehicle reaches a bend, the road is illuminated in an optimum manner. The purpose of the FBL function is to progressively illuminate the verge of the road when the vehicle takes a bend; to this end, an additional light source is provided which progressively supplements the low-beam or high-beam lights during negotiation of a bend;        the so-called Town Light function. This function provides the broadening of a low-beam light type beam whilst slightly reducing its range;        the so-called Motorway Light function. This function provides an increase in the range of a low-beam light;        the so-called Overhead Light function. This function provides a modification of a low-beam light beam so that gantries situated high up are satisfactorily illuminated by means of the low-beam lights;a so-called AWL (Adverse Weather Light) function. This function provides a modification of a low-beam light beam so that the driver is not dazzled by a reflection of his own headlight.        
Optical modules with a fixed or movable shield have been used in the past, and reference can be made in particular to several illustrative examples in the patents EP 1 197 387, EP 1 422 471 or EP 1 422 472. The movable shield, on command and by virtue of the presence of a motor, can take different positions with respect to the light source, including at least one position referred to as optically “active”, that is to say a position where it effectively masks part of the light beam, in particular so that the module emits a beam with a cut-off, such as a low-beam (oblique cut-off) or fog-lamp (horizontal cut-off) type beam. The shield can thus have one or more “active” positions, for example two, one for the right-hand drive low-beam function and one for the left-hand drive function, and also a so-called “passive” function where it does not mask the light beam, thus allowing the module to emit light beams with no cut-off of the high-beam type. For examples of modules with a fixed shield, reference can be made in particular to the patent FR 2 754 039, which describes modules capable of emitting low-beam or fog-lamp beams for example.
Whether the shield is fixed or movable, and irrespective of the type of cut-off it defines in the beam, it remains that all the luminous flux that is intercepted by the shield is lost, and the luminous efficiency, that is to say the ratio between the light emitted by the lamp and that reconstructed at the output of the optical module, is therefore not very satisfactory.
The aim of the invention is then the development of an optical module with a shield of the type described above, in particular of the elliptical type, which has improved optical performance.
One feature of the invention concerns increasing the luminous efficiency of this type of module without impairing the statutory photometric characteristics of the beams with cut-off obtained. Secondarily, the aim of the invention is to achieve this objective without completely changing the design of current optical modules.